JPH077781B2 - How to create a solder joint - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to surface mount technology in the field of electronic mounting, and more specifically to solder ball connectors on the surface of a substrate that is subsequently joined to another electronic structure by a surface mounting process. An improved method for alignment and implementation.

[0002]

Surface mount technology is accepted as the preferred method of joining electronic devices together, especially in high end computers. The pins mounted on the back surface of the ceramic module are pierced into the holes of the circuit board.
Double modules can be placed. Other advantages such as smaller component sizes, higher input / output densities, lower electrical resistance, lower costs, and shorter signal paths have driven the industry to move to surface mount technology.

A myriad of solder structures have been proposed for surface mounting one electronic structure onto another. In a typical surface mount method, a solder structure is formed by screen-printing a solder paste onto a conductive, generally metal pad located on a first electronic structure or "substrate". Align the contact mask with the pad using a stencil printing operation. The solder paste areas on the substrate are aligned with the corresponding pads on the second electronic structure or "circuit board" and placed thereover. Alternatively or additionally, a solder paste may be screen printed onto the pads of the circuit board. After placement, the board and circuit board are subjected to a reflow operation to melt the solder paste and form solder bonds between corresponding pads on the board and circuit board.

Another known surface mount technique uses solder balls rather than solder paste to form the solder structure. The use of solder balls allows a slightly larger amount of solder to be applied more accurately than screen printing. The solder balls are aligned and held on the substrate, which is melted to form solder joints on the conductive pads. As before,
Align the board with the newly joined solder balls with the circuit board. The solder balls are then reflowed to form a good solder bond between the substrate and the circuit board.

However, both the solder paste surface mounting method and the solder ball surface mounting method have drawbacks as the pad density increases. A certain amount of solder must be maintained to obtain a secure solder joint. As the amount of solder required for the pad spacing increases, the solder bridging between the incompatible conductive pads becomes a problem. The problem of bridging becomes significant when a large amount of solder melts during reflow.

Assigned to the applicant of the present invention, 1990 June
One method proposed in U.S. patent application Ser. No. 555120 filed March 18, uses screen printed low melting point solder with a high melting point solder ball.
The above application is incorporated herein by reference. The combined use of solder balls and solder pastes greatly increases the amount of solder that can be placed on the conductive pads due to the increased structural integrity of the solder balls during low melt reflow. The combined use of solder balls and solder paste allows the solder to be tuned to obtain the best electrical, structural and process characteristics. Referring to FIG. 1, as the solder paste 15 that adheres to the conductive pads 16 of the substrate 17, one that melts at a relatively low temperature is selected, while the composition of the solder balls 11 has a high melting point and only a small amount of the solder paste 15 is present during reflow. It melts and fixes the position of the solder ball 11. Since only a small amount of solder is reflowed, there is little risk of bridging, and reliability with a large solder joint is obtained.

However, it has been found difficult to manufacture a solder joint using a solder paste and a solder ball together. Solder balls are difficult to align and manipulate during the reflow process. As a method of handling only solder balls, various methods using vibration, brushing, vacuum, etc. have been proposed in combination with an alignment plate, but when solder paste is added, the process becomes more complicated. Many problems arise in maintaining the centrality of the solder balls between each other and on the substrate, and even the complete loss of the solder balls. If the positions of the solder balls are misaligned, bridging between adjacent pad parts becomes a problem. In one method of making solder joints using the concept of combined solder paste and solder balls, expensive alignment tools have been proposed. At the same time, good alignment between the solder pads, the solder paste and the substrate must be ensured while maintaining the alignment between the substrate pad and the solder joint. Processing time increases rapidly as the number of process inspections increases.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to automate the process of providing a solder structure containing solder paste and solder balls on an electronic board.

Another object of the present invention is to produce a reliable solder joint with reduced bridging between conductor pads.

Another object of the present invention is to reliably align the solder paste and solder ball combination with the substrate pad without the use of expensive alignment tools.

[0011]

The above and other objectives are to provide a measured amount of low melting point on each array of high melting point solder balls held by vacuum in an alignment boat having precisely machined cavities. This is achieved by applying a solder paste. The process flow is summarized as follows. First, place the solder ball in the cavity in the alignment boat and start holding the boat and solder ball in place with vacuum. Second, a quantity of solder paste is applied onto the solder balls in the boat, preferably by screen printing. Thirdly, an alignment plate is placed on the boat which serves as a means for roughly aligning the combination of solder balls and solder paste with respect to the substrate. Fourth, place the substrate on top of the solder balls in the boat through the alignment plate.
Minimal pressure is applied so that the solder paste wets the conductive pads on the substrate. Finally, the substrate and alignment boat assembly is processed in a furnace for solder paste reflow.

During reflow, the substrate can be self-aligned more accurately than the rough alignment by the alignment plate.
Eliminates expensive alignment tools. This is because each portion of the molten solder paste has a natural tendency to wet the entire conductive pad and solder ball on the substrate. Surface tension helps move the substrate into a more precise alignment. Any misalignment that occurs after reflow is usually compensated for during the second reflow when joining the substrate to the circuit board.

[0013]

The present invention can be used to connect solder joints to any component that is joined utilizing surface mount technology. There are many electronic structures within the mounting area, which need to be connected to other similar electronic structures or other mounting levels. For example, an integrated circuit chip is mounted on a metal-coated ceramic substrate. A circuit card with some integrated circuit chips surface mounted is then surface mounted on a circuit board, which is the interconnection circuit to the mainframe computer. Solder balls and solder paste are used as a “substrate” for clarity and consistency.
I will attach it to.

Sometimes referred to as a "circuit board,"
This shall refer to the second electronic structure with which the "substrate" is joined. However, as those skilled in the art will recognize, the present invention could be used to mount solder balls to any number of electronic structures. The bottom of the board is
Having a dielectric portion and a metal portion, the metal portion or pad is used to bond the solder joint. Generally, the dielectric does not adhere to the molten solder.

"Low melting point" (LMP) and "high melting point" (H
The term MP) does not refer to a particular temperature.
The method of the present invention need only have the melting point of the solder paste lower than the melting point of the solder balls. An example of a preferable solder paste / solder ball combination is 37/6.
A eutectic solder paste composed of 3% by weight of Pb / Sn,
It would be a non-eutectic solder composition for solder balls consisting of 90/10 wt% Pb / Sn. The word "eutectic" is lead /
It is the lowest melting point of an alloy consisting of two or more compositions such as tin, and is usually expressed in% by weight. However, a wide range of materials appear suitable for the present invention, many of which are well known in the solder joint art.

Based on the prior art, the first attempt at the solder joining process was made. This is shown in FIGS. 2A-2D.
A vacuum is used to hold the solder balls 11 on the graphite alignment plate 13. Then, after aligning the solder paste mask with the substrate using an optical alignment tool, the substrate 1 is processed as is commonly done in prior art methods.
The eutectic solder paste 15 is screen-printed on the substrate 7 in the pattern of the substrate pad. Next, the board 17 is attached to the solder ball 1
Align to 1. Using the split image optical alignment tool 19, solder paste on the board 17
The pattern 15 is aligned with the solder balls 11 in the X, Y and θ directions. Next, the board 17 is lowered onto the solder 11. Finally, the alignment plate 13, the solder balls 11, the solder paste 15, and the substrate are processed in a furnace with a conveyor to reflow the eutectic solder paste 15 and connect the balls to the substrate pads.

Unfortunately, it has proven difficult and costly to automate the proposed method. Alignment tools, especially split image optical alignment tools, are expensive and the alignment procedure is a major limiting factor in terms of process turnaround time. However, since the ceramic substrate is not cut to a completely uniform size, it was considered necessary to have a tour tool. Prior art alignment systems that do not require a tour system rely on the uniformity of the size and shape of the parts to be aligned.

It has also been found difficult to maintain control of the solder balls with vacuum alone. Not only was it difficult to secure centrality between the solder balls and for the solder paste and the conductive pads on the board,
The solder balls can sometimes be significantly misaligned or even move completely. If the centrality of the solder balls is insufficient, the bridging problem that was intended not to be a combination of the solder paste and the solder balls is likely to occur.

The process flow of the present invention will be described with reference to FIGS. 3A to 3D. In FIG. 3A, the high melting point solder balls 11 are positioned in the cavities 23 of the alignment boat 25. In the preferred embodiment, the solder balls have a diameter of 0.089 mm and are spaced apart from each other by 0.127 mm. However, as will be appreciated by those skilled in the art, the present invention
Applicable to a wide range of solder ball diameters and spacings.
The positioning cavity 23 is formed so as to correspond to the position of each pad on the substrate. For example, on a 25 × 25 mm ceramic substrate, there is an array of 19 × 19 solder pads, so there will be 361 alignment cavities. Cavity 23 holds the solder ball,
An alignment cavity 23A having a diameter slightly larger than the solder ball and a vacuum through hole 23 slightly narrower than the solder ball.
It has two parts, B. According to current manufacturing tolerances, the size of the solder balls is 0.086-0.091 mm, so the ball alignment cavity on the alignment boat is 0.094-0.097 mm. The depth of the cavity is slightly smaller than the diameter of the solder ball. The diameter of the vacuum through hole is not critical as long as a sufficient vacuum force can be maintained on the solder ball 11 to hold it in place. Alignment cavities and vacuum through holes should be designed so that only a small portion of the solder ball, on the order of 0.0076 mm, projects beyond the top surface of the alignment.

Graphite is the preferred material from which the alignment boat 25 is made. Graphite has good thermal conductivity, and its coefficient of thermal expansion is about the same as that of a ceramic substrate. Due to the high thermal conductivity of graphite, the heat of the furnace is transferred to the solder joint, which speeds up the reflow process. Also, high thermal conductivity, which is important for maintaining the uniformity of the bonding composition, helps maintain a uniform reflow temperature on the substrate. Although some ceramic materials may be compatible with alignment boats, they are very expensive to manufacture. Also, while ceramic materials tend to be brittle, graphite materials are much stronger and less prone to cracking.

After the solder balls are seated, a vacuum is introduced to the base of the alignment boat 25 to hold the solder balls 11 and the alignment boat 25 in place. The solder balls are preferably positioned in place with a rubber squeegee. Alignment plate (not shown) with squeegee (not shown) placed on top of alignment boat or top of alignment
Contact across and sweep away excess solder balls.

Referring to FIG. 3B, a portion of the accurately measured low melting point solder paste 15 is screen printed onto the solder ball 11. This step differs from prior art methods of applying solder paste to a relatively large and stable substrate. The successful screen printing of the solder paste on the solder balls was somewhat surprising, if less preferred, given that the solder balls themselves are unwieldy. Solder paste screens are metal contact masks usually punched, perforated, or etched and made of stainless steel, brass, or copper. Stainless steel is the best in terms of wear. If the diameter of the solder ball is 0.089 mm, the diameter of the solder paste part is about 0.076 mm,
The height is 0.025 mm. A solder paste pad 15 having a small diameter and relatively high height has been found to be optimal. The smaller the hole, the better the alignment with the substrate, and the larger the volume, the better the matching between the substrates. It has been observed that when the height of the solder pad is high, a greater proportion of the solder paste in the screen is transferred to the solder ball. Increasing the height may serve somewhat to absorb the warpage in the substrate. For a 25 x 25 mm board with 361 solder joints, the total weight of solder is 0.
163-0.3g is sufficient.

Next, in FIG. 3C, a self-alignment plate 27 is placed on top of the alignment boat 25 in preparation for the substrate 17. The self-aligning plate 27 is a perforated plate that corresponds to the particular substrate being processed. The self-alignment plate 27 roughly aligns the substrate 17 with the solder ball matrix on the alignment boat 25. The "coarse alignment" requirement is met when the solder paste contacts at least a portion of the corresponding pad on the substrate. If less than half of the board pad rests on the solder ball, i.e. the edge of the board pad is in the center of the solder ball,
The method of the present invention forms a reliable bond.
At this point in the method, the near perfect alignment required to make a good solder joint is not necessary. The self-aligning plate 27 is preferably made of stainless steel, but may be any material that is durable, easy to machine and does not release contaminants during the process. Those of ordinary skill in the art will be aware of other means for roughly aligning the substrate with the solder balls.

In FIG. 3D, the substrate 17 is placed on the solder paste pad 15 using the self-aligning plate 27. According to the invention, the substrate 17 can be of any size. For example, a commonly available ceramic substrate for mounting integrated circuits is 25 × 25 mm. The board 17 is pressed into the solder paste 15 with sufficient force so that the board 17 is brought into good contact. 19
25x with 361 solder balls in a 19x array
For a 25 mm square ceramic substrate, about 9.1 to 1
1.3 kg should be sufficient. When sufficient force is applied, the substrate contacts all solder paste pads, resulting in all substrate pads being at least wetted with solder paste. Ceramic substrates often warp, resulting in good solder joints, although the solder paste may lose contact with the substrate after the pressure is released. If the size of the board is different and the number of solder balls is different,
The required power also changes.

The substrate 1 is removed by removing the self-alignment plate 27.
7. The solder balls 11, the solder paste 15, and the alignment boat 25 are passed through a belt-driven furnace. The furnace temperature and residence time are selected so that the low melting point solder paste 15 melts but the high melting point solder ball 11 does not melt.
When using 37/63 wt% Pb / Sn solder paste material, one preferred solder reflow process takes about 13 minutes in the furnace, with dwell times above 183 ° C.
4 minutes, the peak temperature will be below 220 ° C. As the solder paste 15 melts, at least a portion of the misalignment caused by the rough alignment of the substrate with the self-alignment plate 27 due to the surface tension between the solder paste 15, the solder balls 11 and the pads on the substrate 17. Tends to be fixed. Therefore, the method of the present invention does not require expensive split image optical alignment tools. The substrate 17 is then ready for soldering operations to the circuit board or other electronic structure. The misalignment that occurs after reflow is usually compensated for during the second reflow when joining the substrate to the circuit board.

The method of the present invention has several advantages over previous attempts to produce solder paste and solder ball joints based on the prior art. If the solder paste is screen printed onto the pads of the board and then the board is aligned with the solder balls, two viewing systems are required. One is needed to align the solder paste screen with the substrate and the other is required to align the substrate with the solder balls held on the alignment boat. This is because the substrate is not precisely machined unlike the graphite alignment boat,
This is because the dimensions change for each substrate. The second inspection system is the more expensive split image optical alignment system. The present invention does not require a registration system. Since the solder balls are held with high precision in the precision-machined graphite, the mask can be physically aligned with the alignment boat or the alignment means that holds the boat. Is unnecessary. Further, since the surface tension of the melted solder paste serves to correct the positional deviation between the board and the solder ball, and the second reflow is performed at the circuit board level, it is only necessary to roughly align the board. . Therefore, no tour system is required for this step.

The method of the present invention excels in process time. Load solder balls on a flat alignment boat,
Unlike vacuum, which is used only to hold solder balls in place, it is much easier to load solder balls into a recessed boat under vacuum. With the alignment boat of this method, the solder balls are held much more reliably,
It doesn't move easily. This alignment boat is easy to handle,
Because of the holding power, the solder balls are placed in place,
It takes less time to make sure that it remains there and reduces the operator's process time. paste·
Since no additional optical alignment step is required to determine that the screen is aligned with the alignment boat,
The process of forming pads of solder paste on the solder balls is faster. Theoretically, once the alignment boat and solder paste screen were aligned during the initial process inspection, a myriad of substrates could be processed. Similarly, rough alignment of the substrate with the paste-like solder balls also speeds up the process. The method of the present invention is
8 compared to the traditional method of applying solder paste to the board
Estimated to be twice as fast.

Using the present invention, the number of process defects is reduced. Precise machining of the alignment boat allows the centrality between balls to be maintained with high accuracy. The reflow temperature is chosen so that the solder balls do not reflow, so it is essential to hold the solder balls firmly. Traditional methods using planar alignment boats routinely produce 10-50% bridging between substrate pads. With the method of the present invention, solder ball bridging or loss is negligible as long as the substrate is pressed against the solder paste with minimal force and the minimum amount of solder paste is used. The solder joints formed in accordance with the present invention exhibit an improved appearance in both flatness and centrality. The solder joints are flat within 6.5 mils and the solder balls are aligned with each other within 3 mils.

The method of the present invention is much less expensive than the earlier proposed methods because the process time is improved and the tool cost is reduced because the optical alignment tool is no longer needed. Further, since the number of defects in the manufactured substrate is small, the production cost is further reduced. Labor costs are also saved as the process is easy to teach to the operator and requires less process inspection when manufacturing solder joints.

FIG. 4 shows a semi-automatic tool 39 for carrying out the process according to the invention. Tool 39 has a boat locator station 40 on which a graphite alignment boat is mounted. Alignment boat 25 is preferably provided with a sufficient number of solder ball cavities 23 to lay four substrates during a given reflow operation. The tool 39 comprises three plates 50, 60, 70. The first stage is the ball screen printing stage 50, which is the alignment boat 2
Used to screen print solder balls into the alignment cavities within 5. The second stage is the paste screen printing stage 60, which is used to screen print the paste on the solder balls in the alignment boat. Finally, the third step is the alignment locator plate step 70, and the four substrates 17
Is roughly aligned on the alignment boat 25. The pressurizing operation is also performed at this stage. Rows 50, 60 and 70 rotate in turn respectively to boat locator station 40.
Then, it is lowered by a hydraulic cylinder and comes into contact with the alignment boat 25 at each process step.

FIG. 5A is a cross-sectional view of the boat locator plate 41 on the top surface of the boat locator station 40. The other parts of the station 40 have been omitted for clarity. The boat / locator plate 41 is preferably made of stainless steel, and is precision-machined to position the alignment boat 25 in each of the X, Y, and θ directions. As described above, the alignment boat 25 is processed so that it can receive four substrates having specific dimensions and shapes. It is preferable to make all the alignment boats 25 uniform in size and shape, and specially design the pattern of the alignment cavities in accordance with each substrate. A vacuum for fixing the alignment boat 25 and the solder balls is built into the boat locator station 40.

FIG. 5B shows a ball screen printing stage 50.
FIG. 11 is a cross-sectional view of the tool 39 when the tool is brought into contact with the alignment boat 25. Put the assembly of solder balls in the ball reservoir / ball reservoir of the squeegee 51. When the bowl / squeegee 51 crosses the surface of the ball screen plate 53,
The solder balls fall and enter the holes of the ball screen plate 53. Holding plate 55 holds the solder ball in place. The pattern of holes in the ball screen plate 53 matches the pattern of alignment cavities in the alignment boat 25. The thickness of the ball screen plate 53 is close to the diameter of the solder balls so that each hole contains only one solder ball. The ball reservoir / squeegee 51 and the ball screen plate 53 work closely together to prevent solder balls from remaining on the ball screen plate 53 as the squeegee 51 advances. The holding plate 55 is removed, and the solder balls are attached to the inside of the alignment boat 25. Boat 2
A vacuum is maintained to hold 5 and the solder balls in place. All parts of this tool are preferably machined from stainless steel.

Next, the paste screen printing stage 60 is moved to a fixed position. As shown in FIG. 5C, paste
The screen 61 is in contact with the alignment boat 25.
The paste screen 61 is similar to that described above, except that there are holes corresponding to the pad positions of the four substrates. The paste squeegee 63 may be a flat blade made of plastic or rubber. Paste screen 6
It is preferable to sharpen the edge that contacts 1 so that the angle is 45 degrees with respect to the solder screen 61 in each direction. As the squeegee 63 traverses the surface of the screen 61, it applies force to the solder paste through the screen 61 on the top surface of the solder balls. After the paste is applied, the paste screen printing stage 60 is removed from the alignment boat. Hold the solder balls and alignment boat 25 in place with a vacuum.

FIG. 5D is a cross-sectional view of the alignment locator plate step 70 when in contact with the alignment boat 25. The board alignment plate 71 has holes for roughly aligning the four boards 17 with the array of solder paste and solder balls in the alignment boat 25. After placing the boards in place, the module press 73 is brought into contact with the four boards and minimal pressure is applied so that the pads of the board 17 are tightly sealed with solder paste. Square press 73 in the figure
Is preferably a cylinder equipped with a strain gauge for measuring the applied pressure. After the pressure is applied, the press 73 and the alignment locator plate 70 are attached to the substrate 17 and the alignment boat 2.
Move away from 5. The boat and substrate assembly is then placed in a furnace to form a solder joint.

While this invention has been described in terms of its preferred embodiment, modifications can be made without departing from its spirit and scope, as will be appreciated by those skilled in the art.

[0036]

According to the present invention, the surface tension acts when the molten solder paste wets all of the conductive pads on the substrate so that the substrate is at least partially exposed to the array of solder balls during reflow. Since self-realignment is possible, costly alignment is unnecessary.

[Brief description of drawings]

FIG. 1 is a diagram showing a solder joint formed on a substrate from a low melting point solder paste and a high melting point solder ball.

FIG. 2 is a diagram showing each step of a preliminary process for joining a high melting point solder ball to a substrate using a low melting point solder paste.

FIG. 3 is a diagram showing the steps of the process of the present invention for joining high melting point solder balls to a substrate using a low melting point solder paste.

FIG. 4 illustrates a semi-automatic tool for bonding substrates according to the present invention.

5 is a detailed view of three parts of the semi-automatic tool of FIG.

[Explanation of symbols]

 11 solder balls 13 alignment plate 15 solder paste 17 substrate 19 alignment tool 23 alignment cavity 25 alignment boat 27 self-alignment plate 40 boat locator station 50 ball screen printing stage 51 ball reservoir and squeegee 53 ball Screen plate 55 Holding plate 60 Paste screen printing stage 61 Paste screen 63 Squeegee 70 Positioning locator plate stage 73 Module press

 ─────────────────────────────────────────────────── ————————————————————————————————————————————————————————————————————————————————————————————————————————— date ——————−—————————————————————−—————————————————————————————————————— from there, at left? Court 803 (72) Inventor Richard W. Cummings 2437 Jonathan Court, Dumfries, Virginia 22026, USA

Claims (9)

[Claims] 1. A method of making a plurality of solder joints from a combination of a plurality of solder pastes and solder balls to a plurality of conductive pads on one side of a substrate, the method comprising: forming a pattern of the conductive pads on the substrate. Firmly holding a plurality of solder balls in a set of alignment cavities in the alignment means arranged in a corresponding pattern, and applying an amount of solder paste on each of the above solder balls. Forming a plurality of solder paste pads, and the substrate with respect to the solder paste pads such that at least a portion of each of the solder paste pads described above wets a corresponding conductive pad on the substrate. Roughly align and place, press the substrate into the solder paste with minimal force, and lift the solder paste. By chromatography, with the aid of surface tension generated by the solder paste, the method comprising the steps of: causing the substrate aligned with the solder balls. 2. Each of said alignment cavities has a diameter slightly larger than said solder ball, said alignment cavity being connected to a vacuum conduit whose diameter is smaller than said solder ball, and said vacuum The method of claim 1, wherein a vacuum is applied to the conduit to hold the solder balls. 3. The solder paste pad is applied using a solder paste screen having a plurality of holes corresponding to the positions of the solder balls in the alignment cavity. The method described in. 4. The positioning means is a precision-machined graphite boat, and a plurality of positioning cavities having a pattern corresponding to the pattern of the conductive pads on the substrate are formed on one surface of the boat. The method of claim 1, wherein the alignment cavity has a diameter that is slightly larger than the diameter of the solder ball and a depth that is slightly smaller than the diameter of the solder ball. 5. The alignment cavities on the alignment means are arranged in a pattern corresponding to a plurality of substrates and the plurality of substrates are placed in general alignment with the solder paste pads. The method according to claim 1, wherein each of the substrates is pressed into the solder paste. 6. A method of making a plurality of solder joints from a combination of a plurality of solder pastes and solder balls to a plurality of conductive pads on one side of a substrate, the method comprising: forming a pattern of the conductive pads on the substrate. Firmly holding a plurality of solder balls in a set of alignment cavities in the alignment means arranged in a corresponding pattern, and applying an amount of solder paste on each of the above solder balls. Forming a plurality of solder paste pads, and the substrate with respect to the solder paste pads such that at least a portion of each of the solder paste pads described above wets a corresponding conductive pad on the substrate. Roughly align and place, press the substrate into the solder paste with minimal force, and lift the solder paste. By chromatography, with the aid of surface tension generated by the solder paste, the method comprising the steps of: causing the substrate aligned with the solder balls. 7. The solder paste pad is applied using a solder paste screen having a plurality of holes corresponding to the positions of the solder balls in the alignment cavity. The method described in. 8. The aligning means is a precision-machined boat made of flavite, and a plurality of aligning cavities having a pattern corresponding to the pattern of the conductive pads on the substrate are formed on one surface of the boat. 7. The method of claim 6, wherein the alignment cavity has a diameter that is slightly larger than the diameter of the solder balls and a depth that is slightly smaller than the diameter of the solder balls. 9. The alignment cavities on the alignment means are arranged in a pattern corresponding to a plurality of substrates, the plurality of substrates being placed in general alignment with the solder paste pads, 7. The method of claim 6, wherein each of the substrates is pressed into the solder paste.